High voltage direct current HVDC converter device and method for controlling HVDC device

Abstract

A method (100) for controlling a high voltage direct current, HVDC, converter arrangement (1) is provided. The HVDC converter arrangement comprises an upper converter (11) connected between a positive DC pole (21) and an ungrounded common neutral bus (20) and a lower converter (12) connected between a negative DC pole (22) and the ungrounded common neutral bus. The method comprises the steps of: determining (110) a DC voltage difference between a first DC voltage (Upositive) across the upper converter and a second DC voltage (Unegative) across the lower converter; and adjusting (120) the DC voltage (U neutral) at the non-grounded common neutral bus to reduce the DC voltage difference.

Description

Technical Field

[0001] This disclosure generally relates to converter control, and more specifically to the control of HVDC converter devices and systems. Background Technology

[0002] Over the years, the pace of implementing HVDC devices and systems (i.e., systems configured to transmit electrical energy) in transmission networks has been steadily increasing. This pace has been further accelerated by the expanded use of renewable energy sources such as solar and wind power.

[0003] HVDC systems are particularly advantageous when used to transmit electricity generated in remote locations and when power generation is unstable. Therefore, HVDC systems are especially well-suited for transmitting electricity generated from renewable energy sources, particularly when such electricity is generated in remote locations, such as, for example, offshore sites.

[0004] HVDC systems typically include: a first terminal, comprising a converter unit connected to a power plant; and a second terminal, comprising another converter unit connected to a power grid, wherein the first and second terminals are interconnected via HVDC transmission lines.

[0005] During the operation of an HVDC system, i.e., when electrical energy generated at the power plant is transmitted to the transmission network, disturbances may occur. Large disturbances (which may be caused by, for example, the failure or malfunction of one or more converters in a converter unit) can be handled according to strictly defined procedures to ensure the safety of the power plant, the HVDC system, and / or the transmission network. However, such procedures may not be suitable for handling smaller disturbances or disturbances. Known strategies for handling smaller disturbances or disturbances may place an excessive burden on different components of the power plant, the HVDC system, and / or the transmission network.

[0006] Therefore, it is advantageous to provide improved interference control for HVDC systems. Summary of the Invention

[0007] Therefore, the purpose of this disclosure is to provide an HVDC converter device and a method for controlling the HVDC device, which and the method provide improved interference control.

[0008] To achieve this objective, this disclosure provides an HVDC converter device and a method for controlling the HVDC device, as defined in the independent claims. Further embodiments are provided in the dependent claims.

[0009] According to a first aspect of this disclosure, a method for controlling an HVDC converter device is provided. The HVDC converter device includes an upper converter connected between a positive DC terminal and an ungrounded common neutral bus. The HVDC converter device further includes a lower converter connected between a negative DC terminal and the ungrounded common neutral bus. The method includes: determining a DC voltage difference between a first DC voltage across the upper converter and a second DC voltage across the lower converter; and adjusting the DC voltage at the ungrounded common neutral bus to reduce the DC voltage difference.

[0010] According to a second aspect of this disclosure, an HVDC converter device is provided. The HVDC converter includes an upper converter connected between a positive DC terminal and an ungrounded common neutral bus, a lower converter connected between a negative DC terminal and an ungrounded common neutral bus, and a control system. The control system is configured to: determine a DC voltage difference between a first DC voltage across the upper converter and a second DC voltage across the lower converter; and adjust the DC voltage at the ungrounded common neutral bus to reduce the DC voltage difference. It will be understood that the control system may include one or more components and / or subsystems that can be physically arranged at different locations, and wherein the one or more components and / or subsystems may be configured to communicate with each other.

[0011] According to a third aspect of this disclosure, an HVDC system is provided. The HVDC system includes a first HVDC converter device and a second HVDC converter device according to the first aspect. The first HVDC converter device and the second HVDC converter device can be connected via a transmission line.

[0012] Embodiments of this disclosure provide a control technique for the aforementioned (first) HVDC converter device, which can be understood as an ungrounded HVDC converter device. The term "ungrounded" can be understood as the upper and lower converters being connected in series on the DC side of the HVDC converter device, wherein the connection between the converters is not grounded. Thus, the common neutral bus (which can be alternatively understood as, for example, a common neutral station) is the common connection point for the upper and lower converters. Alternatively, the ungrounded HVDC converter device can be understood as a rigid HVDC converter device. Further, the HVDC converter device according to this disclosure can be referred to as a bipolar converter. Therefore, the HVDC converter device according to this disclosure can also be referred to as a rigid bipolar converter. Alternatively, the upper and lower converters can be referred to as a first converter and a second converter, or as a positive converter and a negative converter, respectively.

[0013] Historically, rigid bipolar converters have been controlled to handle small and / or asymmetrical (i.e., at one pole) disturbances by ensuring that the voltage at the common neutral point is kept zero or as close to zero as possible. However, a key insight leading to the inventive concept of this disclosure is that attempting to maintain the voltage at the common neutral point to zero or as close to zero as possible causes unequal power sharing by the converter when small asymmetrical disturbances occur. In other words, by attempting to maintain the voltage at the common neutral point to zero or as close to zero as possible, the voltage across the converter and the active power output by the converter deviate from each other. Consequently, the symmetry of the converter may be lost, and the converter may share unequal amounts of power, which is undesirable because the (nominal) rated power and / or (nominal) rated voltage of the converter can be the same.

[0014] HVDC systems typically consist of a first HVDC converter unit that can be connected to a power plant and a second HVDC converter unit that can be connected to the transmission network. The first and second HVDC converter units are interconnected via HVDC transmission lines. When both HVDC converter units are effectively grounded, the HVDC system can be called a bipolar HVDC converter system or a ground-return bipolar HVDC system. However, when only one of the two HVDC converter units in an HVDC system is effectively grounded, the HVDC system can be called a rigid bipolar HVDC system.

[0015] For a rigid bipolar HVDC system, one HVDC converter unit can be configured to operate in active power control mode, while the other HVDC converter unit can be configured to operate in DC voltage control mode. The HVDC converter unit configured for active power control mode can operate at a specific active power level based on a corresponding active power reference. Furthermore, the HVDC converter unit configured for DC voltage control mode can operate at a DC voltage level, which can be equal to a predetermined value or based on a DC voltage level reference. To maintain stable behavior of the rigid bipolar HVDC system, it may be necessary to ensure that the voltage at the common neutral bus of the ungrounded HVDC converter unit does not fluctuate (i.e., change, vary, and / or oscillate) over time. Historically, this has been accomplished by attempting to keep said voltage at zero. However, it has been recognized that this type of control cannot adequately handle asymmetrical disturbances, such as (small) disturbances on only one pole in an HVDC system, which may cause unequal load sharing by the converter in an ungrounded HVDC unit.

[0016] This disclosure aims to at least partially solve the problems discussed above by providing a proposed control method. Specifically, instead of attempting to maintain the voltage at the common neutral bus at zero, the proposed control method includes adjusting the DC voltage at the common neutral bus to reduce the DC voltage difference between a first DC voltage across the upper converter and a second DC voltage across the lower converter. In other words, this disclosure aims to reduce the DC voltage difference rather than maintain the voltage at the common neutral bus at zero. Thus, this disclosure provides a minimization of the DC voltage difference, such that the DC voltage difference is minimized, i.e., equal to or close to zero. This provides enhanced symmetry with respect to the active power supplied or received by the converters of the HVDC converter device according to this disclosure and / or the voltages across these converters. The improved symmetry results in any increased voltage across the upper and lower converters caused by asymmetrical disturbances or perturbations being shared equally, uniformly, or at least more uniformly by the upper and lower converters. Existing technologies attempt to maintain the voltage at the common neutral bus, thereby causing an overall increase in voltage across either the upper or lower converter. Therefore, this disclosure provides improved control for HVDC systems, and more particularly, improved disturbance control for HVDC systems.

[0017] The upper and lower converters can be configured to operate at active power levels based on a first power reference and a second power reference, respectively. Being configured to operate at active power levels based on power references can be understood as being configured to operate according to an active power mode. Operating the upper and lower converters according to an active power mode facilitates adjustment of the DC voltage differential, or in other words, it facilitates floating-point operation of the common neutral bus.

[0018] Adjusting the DC voltage at the ungrounded common neutral bus may include: calculating a power reference difference based on a determined DC voltage difference; updating a first power reference to be equal to a predetermined power reference plus or minus the power reference difference; and updating a second power reference to be equal to a predetermined power reference minus or plus the power reference difference. The term "power reference" may be understood as, but is not limited to, an active power reference. Adjusting the power supplied or absorbed by the first HVDC converter unit can be performed by controlling the switching of the converter in the first HVDC converter unit to change the on-time and off-time of the switches, thereby supplying or absorbing more or less power.

[0019] When the first power reference is updated to equal the predetermined power reference plus the power reference difference, the second power reference can be updated to equal the predetermined power reference minus the power reference difference. Correspondingly, when the first power reference is updated to equal the predetermined power reference minus the power reference difference, the second power reference can be updated to equal the predetermined power reference plus the power reference difference. In other words, the first and second power references can be updated in opposite directions with respect to the power reference difference. Alternatively, the first and second power references can be balanced with respect to the power reference difference.

[0020] Adjusting the DC voltage at the ungrounded common neutral bus may include: calculating a current difference based on the determined DC voltage difference; updating a first active current reference to be equal to the active current reference plus or minus the current difference; and updating a second active current reference to be equal to the active current reference minus or plus the current difference. Alternatively, adjusting the DC voltage at the ungrounded common neutral bus may include: calculating an angle difference based on the determined DC voltage difference; updating a first angle reference to be equal to the angle reference plus or minus the angle difference; and updating a second angle reference to be equal to the angle reference minus or plus the angle difference.

[0021] As described above, one advantage of adjusting the DC voltage at the common neutral bus based on current difference or angle difference is that it allows HVDC converter units to be configured to operate in active power mode or DC voltage control mode.

[0022] A first HVDC converter unit capable of operating in active power mode can be connected via a transmission line or cable to a second HVDC converter unit capable of operating in DC voltage control mode. In such an HVDC system (i.e., including a first HVDC converter unit and a second HVDC converter unit), the second HVDC converter unit can be considered as being configured to maintain a predetermined DC voltage at the DC terminal of the system, which includes the positive DC terminal and the negative DC terminal of the first HVDC unit.

[0023] If the DC voltage difference is higher than a predetermined value, the method may include the step of using a surge arrester to limit the DC voltage at the ungrounded common neutral bus. Accordingly, the HVDC converter device may include a surge arrester, and the control system may also be configured to use a surge arrester to limit the DC voltage at the ungrounded common neutral bus. The surge arrester may be able to provide handling of larger disturbances. Therefore, this disclosure may be able to provide improved handling of both large and small disturbances. This can thus provide an increased level of safety and / or control.

[0024] The method may further include receiving the DC voltage across the upper converter and the DC voltage across the lower converter, and the control system may be further configured to receive the DC voltage across the upper converter and the DC voltage across the lower converter. The DC voltages across the upper and lower converters can be measured. This measurement may include measuring the voltage at the positive DC terminal, the negative DC terminal, and / or the neutral common bus. The DC voltage across the upper converter can be understood as the voltage difference between the voltage at the positive DC terminal and the voltage at the common neutral bus, and the DC voltage across the lower converter can be understood as the voltage difference between the voltage at the common neutral bus and the negative DC terminal. Therefore, the DC voltages across the upper and lower converters can correspond to the measured voltage difference.

[0025] The DC voltage across the upper converter and the DC voltage across the lower converter can be received within a predetermined time interval. Furthermore, the DC voltage across the upper and lower converters can be measured within the predetermined time interval. Thus, the time delay for receiving the DC voltage can be less than or equal to the predetermined time interval. The DC voltage can be represented by a signal receivable by a control system configured to control the HVDC converter apparatus and system according to this disclosure. The performance of the method disclosed herein can be improved by receiving the DC voltage across the converter within a shorter time interval or with a shorter delay. The predetermined time interval can be less than, for example, 20 milliseconds, or preferably less than 10 milliseconds.

[0026] The rated voltages of the upper and lower converters can be the same. The term "voltage" can be understood as, but is not limited to, the nominal voltage. The rated voltages of the upper and lower converters can be similar. In other words, the rated voltages of the upper and lower converters can differ from each other by 0% to 10%, or preferably by 0% to 5%, and more preferably by 0% to 1%.

[0027] HVDC converter units can be configured to be connected to another HVDC converter unit via positive and negative DC terminals. The two HVDC converter units can be connected via a transmission line or cable. The other HVDC converter unit can be configured to operate in DC voltage mode and provide or supply predetermined DC voltage levels at the positive and negative DC terminals.

[0028] Other objects, features, and advantages of the accompanying embodiments will become apparent from the following detailed disclosure, the appended dependent claims, and the accompanying drawings. Attached Figure Description

[0029] This and other aspects of the present disclosure will now be described in more detail with reference to the accompanying drawings, which illustrate multiple embodiments of the present disclosure.

[0030] Figure 1 and Figure 2 An HVDC system according to an exemplary embodiment of the present disclosure is illustrated schematically.

[0031] Figure 3a , Figure 3b and Figure 3c A control system according to an exemplary embodiment of the present disclosure is illustrated schematically.

[0032] Figure 4 A flowchart of a method according to an exemplary embodiment of the present disclosure is shown. Detailed Implementation

[0033] Figure 1 An HVDC system 55 according to an exemplary embodiment of the present disclosure is illustrated schematically.

[0034] HVDC system 55 includes a first HVDC converter unit 1 and a second HVDC converter unit 4. The first HVDC converter unit 1 and the second HVDC converter unit 4 are connected via a transmission line. Figure 1 The middle line is indicated as a solid line.

[0035] The first HVDC converter unit 1 includes an upper converter 11 and a lower converter 12 connected in series on the DC side of the first HVDC converter unit 1. The upper converter 11 is connected between the positive DC terminal 21 and the common neutral bus 20, and the lower converter 12 is connected between the negative DC terminal 22 and the common neutral bus 20. The common neutral bus 20 is not grounded, and the neutral voltage U at the common neutral bus 20 is... 中性 It can be understood as floating.

[0036] The upper converter 11 and the lower converter 12 each have Figure 1 The image is shown as passing through the respective current sources (each in...) Figure 1 (shown as two overlapping circles) connected to voltage source U s The upper pole 21 and lower pole 22 of converters 11 and 12 are in Figure 1 The diagram shows poles 21 and 22 located on the transmission line connecting the first HVDC converter unit 1 and the second HVDC converter unit 4. However, it is understood that poles 21 and 22 could be the locations where converters 11 and 12 are connected to the transmission line on the DC side of the HVDC unit 1.

[0037] The first DC voltage U across the upper converter 正 Indicated by the arrow extending from the common neutral bus 20 to the upper pole 21. Correspondingly, the second DC voltage U across the lower converter... 负 Indicated by the arrow extending from the common neutral bus 20 to the lower pole 22.

[0038] The second HVDC converter unit 4 includes an upper converter 41 and a lower converter 42. The upper converter 41 of the second HVDC converter unit 4 is connected between the transmission line to which the upper converter 11 of the first HVDC converter unit 1 is connected and ground. Correspondingly, the lower converter 42 of the second HVDC converter unit 4 is connected between the transmission line to which the lower converter 12 of the first HVDC converter unit 1 is connected and ground. Further, each of the converters 41 and 42 is configured to be connected on the AC side to a power grid or substation. Figure 1 The dashed lines extending outward from converters 41 and 42 indicate this.

[0039] Figure 2 An HVDC system 65 according to an exemplary embodiment of the present disclosure is illustrated schematically.

[0040] Figure 2 The HVDC system 65 shown includes... Figure 1 The HVDC system shown has similar features and components. Therefore, reference is made to... Figure 1 Related descriptions are provided to enhance understanding.

[0041] like Figure 2 The HVDC system 65 shown is with Figure 1 The difference between the HVDC systems shown is that the second HVDC converter unit 4 consists of two ideal DC sources U. dc Instead of the upper and lower converters (such as...) Figure 1 (As shown in the diagram). This illustration depicts the second HVDC converter unit 4 configured to operate in a DC voltage control mode, which allows the converter of the second HVDC converter unit 4 to be modeled or represented as an ideal DC source U. dc The converter of the second HVDC converter unit 4 is modeled as an ideal DC source U. dc This facilitates improved control of the first HVDC converter unit 1. The ideal DC source U illustrated is... dc Ensure: Positive current I 正 The current flows through one of the two transmission lines and via the upper pole 21 to the upper converter 11 of the first HVDC converter unit 1, and the negative current I 负 It flows through the other of the two transmission lines and via the lower pole 22 to the lower converter 12 of the first HVDC converter unit 1.

[0042] Another difference is, Figure 2 The simulated interference voltage u is shown. 模拟 .exist Figure 2 In the simulation, the interference voltage u 模拟It is shown as a transmission line connected to the upper converter 11. However, it will be understood that this is only an example, and it could be shown as a transmission line connected to the lower converter 12. Simulated interference voltage u 模拟 This can be understood as representing or simulating actual interference (or disturbance). Further, the simulated interference voltage u shown... 模拟 It is an asymmetric interference because it only affects one of the converters 11 and 12, namely the upper converter 11 in this exemplary embodiment.

[0043] If as Figure 2 The HVDC system 65 shown (which is subjected to simulated interference voltage u) 模拟 The effect) is controlled by methods and / or control systems based on existing technology, then such methods or control systems will attempt to reduce the neutral voltage U at the common neutral bus 20. 中性 The voltage is maintained at or near zero in an attempt to maintain the stability of the first HVDC converter unit 1. However, efforts are made to keep the neutral voltage U... 中性 Maintaining a value of zero would cause the converters 11 and 12 of the first HVDC converter unit 1 to lose symmetry. For example, the rated DC voltage of converters 11 and 12 could be 525 kV, and the rated power of the converter could be 1000 MW. The ideal DC source U illustrated is... dc Rated DC voltage (i.e., 525 kV) can be supplied to converters 11 and 12. However, when a simulated interference voltage u is introduced... 模拟 (For example, it can be equal to 5 kV) then the voltage at the upper pole 21 will be equal to that of the ideal DC source U shown in the diagram. dc The provided voltage plus the simulated interference voltage u 模拟 (In this example, the voltage at the upper pole 21 is equal to 530 kV). According to existing methods and / or control systems, the active power references of the upper converter 11 and the lower converter 12 will first be adjusted to attempt to bring the neutral voltage U... 中性 The value remains zero. Therefore, the upper converter 11 and the lower converter 12 will operate at different active power levels. More specifically, in this example, the upper converter 11 will operate at a power level above its rated power, and the lower converter 12 will operate at a power level below its rated power to maintain the neutral voltage U. 中性 It remains at zero. Furthermore, this type of operation will subsequently cause the voltage U across the upper converter 11 to... 正 Equal to the ideal DC source U dc Add simulated interference voltage u 模拟 (i.e., U 正 (equal to 530 kV), while the voltage U across the lower converter 12 负 It will remain at 525 kV, which is equal to the ideal DC source U.dc Therefore, regarding the voltage U across converters 11 and 12... 正 U 负 The symmetry will be lost. In this example, the upper converter 11 will operate at a voltage 5 kV higher than its rated voltage, while the lower converter 12 will operate at its rated voltage. Consequently, the upper converter 11 will experience significantly greater wear than the lower converter 12, which may increase the risk of future failure of the upper converter 11 (i.e., the converter directly experiencing asymmetrical disturbances). In this example, the upper converter 11 will operate at a voltage higher than its rated voltage and a power higher than its rated power, while the lower converter 12 will operate at its rated voltage and a power lower than its rated power. In summary, the prior art has proposed methods and control systems that lead to the loss of symmetry, which in turn leads to excessive and unbalanced wear on converters 11 and 12.

[0044] In contrast to existing technologies, this disclosure provides an improved method and control system designed to control the voltage U across converters 11 and 12. 正 U 负 The difference between them remains zero or close to zero, thereby reducing or minimizing the DC voltage difference. If the first HVDC device 11 is subject to the example discussed above (where the ideal DC source U...) dc Provide the rated DC voltage (i.e., 525 kV) for converters 11 and 12 and simulate the interference voltage u. 模拟 The results will be greatly improved if the voltage U is supplied to the upper converter 11 and controlled by the method and control system according to this disclosure. Firstly, the proposed method and control system can be configured to continuously or intermittently measure and compare the voltage U across the converters 11, 12. 正 U 负 Therefore, this embodiment allows for the determination of the DC voltage U across the upper converter 11. 正 The DC voltage U across the lower converter 12 负 The DC voltage difference between them allows for adjustment of the DC voltage U at the common neutral bus 20. 中性 This reduces the DC voltage difference. In the example discussed, the DC voltage U at the common neutral bus 20 can be reduced. 中性 Adjusting it to 2.5 kV will cause the voltage U across converters 11 and 12 to change. 正 U 负This equals 527.5 kV. Correspondingly, the DC voltage difference will be zero. Since converters 11 and 12 are configured to operate in active power mode, the active power output will be equal for both converters 11 and 12. However, both converters 11 and 12 will operate at voltages higher than their rated voltages. Nevertheless, compared to the prior art, both converters 11 and 12 will operate at voltages 2.5 kV higher than their rated voltages, instead of one of the converters operating at 5 kV higher than its rated voltage (i.e., twice as high). Therefore, both converters 11 and 12 will experience the same amount of wear, and this wear will be significantly reduced (halved in this example) compared to the wear caused by methods and control systems in the prior art. In other words, the embodiments of this disclosure provide improved symmetry compared to the prior art.

[0045] Figure 3a A control system 70a according to an exemplary embodiment of the present disclosure is illustrated schematically.

[0046] The control system 70a includes a first part 71 and a second part 72. Both the first part 71 and the second part 72 receive an HVDC converter device (not shown; see example) according to the first aspect of this disclosure. Figure 1 and Figure 2 The positive voltage U across the upper converter of the circuit. 正 and an HVDC converter device according to the first aspect of this disclosure (not shown; see example) Figure 1 and Figure 2 The negative voltage U across the lower converter of the circuit. 负 Then, the first part 71 and the second part 72 are configured to calculate the voltage difference U. 差 The voltage difference is equal to the upper voltage U. 正 Subtract the negative voltage U 负 The first part 71 and the second part 72 of the control system 70a may further each include a calculation unit 73, which can be configured to calculate the voltage difference U. 差 To calculate the power reference difference P 差 Part 71 is configured to use the calculated voltage difference U 差 Compared with the predetermined power reference P 参考 Add them together to calculate or update the first power reference P. 参考,11 Accordingly, the second part 72 is configured to pass the calculated voltage difference U 差 Compared with the predetermined power reference P 参考 Add them together to calculate or update the second power reference P. 参考,21 .

[0047] The first part 71 and the second part 72 of the control system 70a can be configured to control corresponding converters 11, 12 in the upper converter 11 and the lower converter 12. Further, the first part 71 and the second part 72 of the control system 70a can be implemented in a (i.e., a single) control unit, or alternatively in separate units.

[0048] It will be understood that even if control system 70a or a part of control system 70a is in Figure 1 and Figure 2 The diagram is not clearly shown in the text. Figure 1 and Figure 2 The systems and / or devices shown may also include control systems or portions thereof. For example, the systems and / or devices may include hardware and / or computing units configured to operate control system 70a or portions thereof. Further, control system 70a or portions thereof may be communicatively connected to components of the systems and / or devices to allow measurement of signals, voltages, and / or currents. Additionally, control system 70a or portions thereof may be configured to receive signals from and / or transmit signals to the systems and devices.

[0049] Figure 3b A control system 70b according to an exemplary embodiment of the present disclosure is shown.

[0050] Figure 3b The control system 70b shown includes a... Figure 3a The control system shown has similar features and components. Therefore, reference is made to... Figure 3a Related descriptions to enhance understanding.

[0051] The control system 70b includes a first part 81 and a second part 82, both of which receive an HVDC converter device (not shown; see example) according to a first aspect of this disclosure. Figure 1 and Figure 2 The positive voltage U across the upper converter of the circuit. 正 and an HVDC converter device according to the first aspect of this disclosure (not shown; see example) Figure 1 and Figure 2 The negative voltage U across the lower converter of the circuit. 负 And is configured to calculate voltage difference U 差 The voltage difference is equal to the upper voltage U. 正 Subtract the negative voltage U 负 .

[0052] Control system 70b and Figure 3a The difference between the control systems shown is that the calculation unit 73 of the first part 81 and the second part 82 is configured based on the calculated voltage difference U.差 To calculate the current difference I 差 .

[0053] The first part 81 is configured to pass the current difference I 差 With active current reference Id 参考 Add them together to calculate or update the first active current reference Id. 参考, 11 The second part 82 is configured to pass the current difference I 差 With active current reference Id 参考 Add them together to calculate or update the second active current reference Id. 参考, 12 .

[0054] Active current reference Id 参考 This could be the d-component of the active current reference in the dq domain. Furthermore, when transitioning from the ABC domain to the dq domain, the predetermined power reference P... 参考 Can be compared with active current reference Id 参考 Proportional. Therefore, the first active current reference Id 参考, 11 Second active current reference Id 参考, 12 Can be compared with the first power reference P 参考,21 Second power reference P 参考,22 Proportional.

[0055] Therefore, the control system 70b can be configured to provide an alternative method for adjusting the DC voltage at the common neutral bus, which may include: based on the determined DC voltage difference U 差 To calculate the current difference I 差 The first active current reference Id 参考, 11 Updated to equal active current reference Id 参考 Add or subtract the current difference I 差 and the second active current reference Id 参考, 12 Updated to equal active current reference Id 参考 Subtract or add current difference I 差 .

[0056] Figure 3c A control system 70c according to an exemplary embodiment of the present disclosure is shown.

[0057] Figure 3c The control system 70c shown includes a... Figure 3a and Figure 3b The control system shown has similar features and components. Therefore, reference is made to... Figure 3a and Figure 3b Related descriptions to enhance understanding.

[0058] The control system 70c includes a first part 91 and a second part 92, both of which receive an HVDC converter device (not shown; see example) according to a first aspect of this disclosure. Figure 1 and Figure 2 The positive voltage U across the upper converter of the circuit. 正 and an HVDC converter device according to the first aspect of this disclosure (not shown; see example) Figure 1 and Figure 2 The negative voltage U across the lower converter of the circuit. 负 And is configured to calculate voltage difference U 差 The voltage difference is equal to the upper voltage U. 正 Subtract the negative voltage U 负 .

[0059] Control system 70c and Figure 3a and Figure 3b The difference between the control systems shown is that the calculation unit 73 of the first part 81 and the second part 82 is configured based on the calculated voltage difference U. 差 To calculate the angle difference θ 差 .

[0060] Part 91 is configured to use the angle difference θ 差 With angular reference θ 参考 Add them together to calculate or update the first angle reference θ. 参考, 11 Part 92 is configured to pass the angle difference θ 差 With angular reference θ 参考 Add them together to calculate or update the second angle reference θ 参考, 12 .

[0061] According to the standard power angle equation, the active power transfer between two sources is proportional to the angle difference between the two sources. For the purposes of this disclosure, the two sources can be understood as either a power grid or a source (in...). Figure 1 and Figure 2 The middle indicator is U s ), converter (in Figure 1 and Figure 2 The components (11 and 12) are connected to the power grid or source on the AC side. Therefore, this disclosure may include measuring, receiving, and / or calculating the angle(s) at the two sources, as defined above.

[0062] Therefore, the predetermined power reference P 参考 Can be compared with the angle difference θ 差 Proportional. Therefore, the first angle reference θ 参考, 11 Second angle reference θ 参考, 12 Can be compared with the first power reference P 参考,21 Second power reference P 参考,22 Proportional.

[0063] Therefore, the control system 70c can be configured to provide an alternative method for adjusting the DC voltage at the common neutral bus, which may include: based on the determined DC voltage difference U 差 To calculate the angle difference θ 差 , with the first angle reference θ 参考, 11 Updated to equal angle reference θ 参考 Add or subtract the angle difference θ 差 and referencing the second angle θ 参考, 12 Updated to equal angle reference θ 参考 Subtract or add the angle difference θ 差 .

[0064] Figure 4 A flowchart of a method 100 according to an exemplary embodiment of the present disclosure is shown.

[0065] Method 100 is used to control an HVDC converter device according to a second aspect of the present disclosure. Method 100 includes the steps of: determining a DC voltage difference between a first DC voltage across an upper converter at 110 and a second DC voltage across a lower converter; and adjusting the DC voltage at a common neutral bus at 120 to reduce the DC voltage difference.

[0066] The steps of adjusting the DC voltage at the 120 common neutral bus may include the following (sub) steps: calculating the 121 power reference difference based on the determined DC voltage difference, updating the first power reference 122 to be equal to a predetermined power reference plus or minus the power reference difference, and updating the second power reference 123 to be equal to a predetermined power reference minus or plus the power reference difference.

[0067] Further, method 100 may include: in response to determining that the DC voltage difference is higher than a predetermined value, using a surge discharger to limit the DC voltage at the 111 common neutral bus.

[0068] Generally, unless otherwise expressly defined herein, all terms used in the claims shall be interpreted according to their ordinary meaning in the art. Unless otherwise expressly stated, all references to “a / an / the element, device, component, apparatus, module, action, etc.” shall be openly interpreted as referring to at least one instance of an element, device, component, apparatus, module, action, etc. Unless expressly stated otherwise, the actions of any method disclosed herein need not be performed in the exact order disclosed.

[0069] Although the invention has been illustrated in the accompanying drawings and foregoing description, such illustrations are to be considered illustrative or exemplary rather than restrictive; the invention is not limited to the disclosed embodiments. Other variations of the disclosed embodiments can be understood and implemented by those skilled in the art in practicing the claimed invention by studying the drawings, the disclosure, and the appended claims. In the appended claims, the word "comprising" does not exclude other elements or steps, and the indefinite articles "a" or "an" do not exclude multiple. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that combinations of these measures cannot be advantageously used. Any reference numerals in the claims should not be construed as limiting the scope.

Claims

1. A method (100) for controlling a high-voltage direct current (HVDC) converter device (1), wherein, The HVDC converter device includes: Upper converter (11) connected between the positive DC terminal (21) and the ungrounded common neutral bus (20). The lower converter (12) is connected between the negative DC pole (22) and the ungrounded common neutral bus. The method includes: Determine (110) the first DC voltage (U) across the upper converter. 正 ) and the second DC voltage (U) across the lower converter 负 The DC voltage difference between them; and Adjust (120) the DC voltage (U) at the ungrounded common neutral bus. 中性 This reduces the DC voltage difference.

2. The method according to claim 1, wherein, The upper converter and the lower converter are configured to be based on a first power reference (P). 参考, 11 ) and second power reference (P 参考, 21 It operates at the active power level.

3. The method according to claim 2, wherein, The steps for adjusting the DC voltage at the ungrounded common neutral bus include: The power reference difference (P) is calculated based on the determined DC voltage difference. 差 ); The first power reference is updated (122) to be equal to the predetermined power reference (P). 参考 Add or subtract the power reference difference; and The second power reference is updated (123) to be equal to the predetermined power reference minus or plus the power reference difference.

4. The method according to claim 1, wherein, The steps for adjusting the DC voltage at the ungrounded common neutral bus include: The current difference (I) is calculated based on the determined DC voltage difference. 差 ); The first active current reference (Id) 参考, 11 Updated to equal the active current reference (Id) 参考 Add or subtract the current difference; and The second active current reference (Id) 参考, 12 The current is updated to be equal to the active current reference minus or plus the current difference; or The step of adjusting the DC voltage at the ungrounded common neutral bus includes: The angle difference (θ) is calculated based on the determined DC voltage difference. 差 ); Reference the first angle (θ) 参考, 11 Updated to equal angle reference (θ) 参考 Add or subtract the angle difference; and Reference the second angle (θ) 参考, 12 The value is updated to be equal to the angle reference minus or plus the angle difference.

5. The method according to any one of claims 1 to 4, further comprising the following steps: Receives the DC voltage at both ends of the upper converter (101) and the DC voltage at both ends of the lower converter (102).

6. A high-voltage direct current (HVDC) converter device (1), comprising: Upper converter (11) connected between the positive DC pole (21) and the ungrounded common neutral bus (20); A lower converter (12) connected between the negative DC terminal (22) and the ungrounded common neutral bus; and a control system (70a-c), wherein the control system is configured to: Determine the first DC voltage (U) across the upper converter. 正 ) and the second DC voltage (U) across the lower converter 负 The DC voltage difference between them; as well as Adjust the DC voltage (U) at the ungrounded common neutral bus. 中性 This reduces the DC voltage difference.

7. The HVDC converter device according to claim 6, wherein, The upper converter and the lower converter are configured to be based on a first power reference (P). 参考, 11 ) and second power reference (P 参考, 21 It operates at the active power level.

8. The HVDC converter device according to claim 7, wherein, The control system is configured to adjust the DC voltage at the ungrounded common neutral bus by performing the following operations: The power reference difference (P) is calculated based on the determined DC voltage difference. 差 ); Update the first power reference to be equal to the predetermined power reference (P). 参考 Add or subtract the power reference difference; as well as The second power reference is updated to be equal to the predetermined power reference minus or plus the power reference difference.

9. The HVDC converter device according to claim 6, wherein, The control system is configured to adjust the DC voltage at the ungrounded common neutral bus by performing the following operations: The current difference (I) is calculated based on the determined DC voltage difference. 差 ); The first active current reference (Id) 参考, 11 Updated to equal the active current reference (Id) 参考 Add or subtract the current difference; as well as The second active current reference (Id) 参考, 12 The current is updated to be equal to the active current reference minus or plus the current difference; or The control system is configured to adjust the DC voltage at the ungrounded common neutral bus by performing the following operations: The angle difference (θ) is calculated based on the determined DC voltage difference. 差 ); Reference the first angle (θ) 参考, 11 Updated to equal angle reference (θ) 参考 Add or subtract the angle difference; as well as Reference the second angle (θ) 参考, 12 The value is updated to be equal to the angle reference minus or plus the angle difference.

10. The HVDC converter device according to any one of claims 7 to 9, further comprising a surge arrester connected to the ungrounded common neutral bus, and wherein, The control system is also configured to: If the DC voltage difference is higher than a predetermined value, the surge discharger is used to limit the DC voltage at the ungrounded common neutral bus.

11. The HVDC converter device according to any one of claims 7 to 10, wherein, The control system is also configured to receive DC voltages at both ends of the upper converter and DC voltages at both ends of the lower converter.

12. The HVDC converter device according to claim 11 or the method according to claim 5, wherein, The DC voltages at both ends of the upper converter and the lower converter are received within a predetermined time interval.

13. The HVDC converter device according to any one of claims 7 to 12, wherein, The upper converter (11) and the lower converter (12) have the same rated voltage.

14. The HVDC converter device according to any one of claims 7 to 13, wherein, The HVDC converter unit is configured to be connected to another HVDC converter unit via the positive DC terminal (21) and the negative DC terminal (22).

15. An HVDC system (55) comprising a first HVDC converter unit (1) according to any one of claims 7 to 14, and a second HVDC converter unit (4), wherein, The first HVDC converter unit and the second HVDC converter unit are connected via a power transmission line.

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